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This article reports that rapid recolonization can be a major problem for the management of overabundant populations if the removal techniques are short term. Continuous removal of individuals minimize rapid recolonization, but it could profoundly alter the population's composition and may in fact separate individuals of high quality from individuals of low quality. If residents were removed and immigration occurred quickly, immigrants would be present in the population and create a bias towards individuals of low quality, assuming that immigrants are of low quality. Trap barrier systems (TBS) were introduced to some Southeast Asian countries for rodent management. If a TBS removed mainly dispersers of low quality and left the resident population intact, the quality of residents near a TBS would be similar to rats in areas without a TBS. Researchers selected 6 experimental plots in irrigated rice monoculture. Each plot was adjacent to a main irrigation channel of 6-m width. The fumigation of burrows was thought to yield residents. Rats were fumigated and dug out of their burrows in the centre of 1 quadrant of the semicircle per trapping session in treatment plots and control plots.

Fertility control is used for the management of overabundant species. If sterilized individuals abandon their territories, fertile immigrants may invade and compromise fertility control. In southeast Asia, ricefield rats (Rattus argentiventer) can cause significant pre-harvest damage to lowland irrigated rice fields and may be a prime target for the use of fertility control. However, little is known about the behavioral response of ricefield rats to sterilization. We tested the effects of surgical and hormonal sterilization on movement patterns of female ricefield rats in rice fields in West Java, Indonesia. We found that surgically sterilized rats had the largest home ranges (1.8 &plumn; 0.1 ha), about twice the size of home ranges of hormonally sterilized rats and fertile rats. Hormonally sterilized rats tended to lose their territories--indicated by a high rate of burrow relocation--although hormonally sterilized, surgically sterilized, and fertile rats did not leave the ricefield system. We found no difference in survival rate and preference for refuge habitats between sterilized and fertile rats. Although changes in movement patterns after sterilization occurred, these changes are unlikely to affect the success of fertility control in ricefield rats negatively because sterilized rats remained in the ricefield system throughout the breeding period. [ABSTRACT FROM AUTHOR]

For the sustainable management of small mammals, fertility control may be used in the future. Little is known about what proportions of females need to be sterilized to achieve an impact on population size and what compensatory processes may act on the population level. We tested the impact of surgical sterilization of zero, 25, 50, and 75% of females on the population dynamics and demography of enclosed populations of ricefield rats (Rattus argentiventer) and damage to rice crop. Sterilizing 50% of female founders (6 of 12) decreased population size at the end of the breeding season by about 50%. We used a simulation model, based on the breeding biology of the ricefield rat in the field and in the control enclosures, to generate the expected dynamics of the enclosure populations. The results suggested that compensation occurred in the enclosures where 75% of female founders (9 of 12) had been sterilized. We detected a slight tendency for 50% higher numbers of recent uterine scars in fertile founder females in the 50% and 75% treatments versus 25% treatments and controls (P = 0.198). The primary demographic mechanism for compensation was higher survival of young rats in enclosures where 75% of females were sterilized. However, compensation only partially offset the decrease in population size. We found no conclusive evidence that the reproductive output of F[sub1] generation females was higher when large proportions of female founders were sterilized. Early in the breeding season, the per capita damage to rice plants in populations without sterilized ricefield rats was increased. Our results suggest that the sterilization of >50% of females in ricefield rat populations can reduce rat population growth and rat damage to rice crops. [ABSTRACT FROM AUTHOR]